Networks in More Detail
The boxes that make a network work
Work out what a hub, a switch, a router, a modem and an access point each do, and choose the one a job needs.
Every box sitting between two machines is answering the same question — where does this message go next? — and what separates them is how much each one knows when it answers. Some know nothing at all and pass the question on by shouting. Some keep a note of which machine is on which of their sockets and answer precisely. Some know about whole networks rather than machines, and their answer is which network to try next rather than which cable. And some are not deciding anything: they exist to turn a message into a form that some particular kind of line can carry, and to turn it back at the far end.
Knowing nothing versus keeping a note
The oldest device in this list keeps no note of anything, so when a message arrives it has no way of telling which cable the message ought to go down — and repeating it down all of them is the only honest thing left to do. A newer device watches which machine is on which socket, writes it down, and uses the note. Nothing about the cables changed between the two; the whole difference is a note. This is worth spelling out because it is where the traffic on a network comes from: on the older kind, every conversation is heard by everybody, and all of that is cable being used up by machines that were never being spoken to.
Worked example
A computer in one office needs to reach a machine in a different office, on a different network. Which devices does the message meet?
The computer hands the message to whatever it is plugged into, and asks for it to be delivered.
A machine never works out the whole journey itself. It knows one step, and hands the problem over.
Try it together
Now work through the traffic together. Nine computers are plugged into a hub, which repeats every message out to every other machine on it.
Count copies, one message at a time.
1.One computer sends one message. How many copies of it leave the hub?
Have a go
Have a go on your own. A device is added so that a tablet with no socket on it can join the lab network. Which device is it?
Ready to practice?
Eight questions on what you have just read. Nothing is timed, and you can play as many times as you like.